Smoke detectors

ABSTRACT

A smoke detector unit ( 20 ) comprising a housing containing a smoke detector ( 24 ) and at least two component mounting boards, such as printed circuit boards, in a stacked arrangement, the housing having at least one air gap ( 34 ), wherein one of the boards ( 36 ) is inverted with respect to the other and the detector is positioned on the lower board whereby, in use, the detector extends upwardly between the boards. The housing may be in the form of a ceiling rose.

The present invention relates to an improved smoke detector,particularly but not exclusively a smoke detector for use in domesticsituations.

It is known to provide a smoke detector within a housing for attachmentto a ceiling, the housing containing a smoke chamber together with thenecessary control unit, power supply and sounder to alert the occupantsof a possible fire in the event that smoke is detected. However, suchhousings tend to be of a relatively large size in order to accommodatethe components, in particular the smoke chamber, which results in theunit being detrimental to the decor of the building. This also preventsadditional components being included in the unit, for example to allowthem to function as a ceiling rose or to incorporate, say, thecomponents for an emergency light or other type of detector. In the caseof a ceiling rose, the requirement for a central wire to pass through acircular unit means that the largest component, usually the smokedetector, dictates the minimum diametric size of the unit. Thus,following the conventional teaching, providing for multiple functionswould only serve to increase the size of the unit further. As a result,although a number of earlier documents dating back many years, such asGB 2189634 (Lawrence Benson), U.S. Pat. No. 4,090,178 Elwood G. Norris)and U.S. Pat. No. 4,717,910 Keith A. Scripps et al) disclose the generalconcept of providing a combined ceiling rose and smoke detector, sucharticles are still not available in the marketplace due to earlierinvestigations failing to overcome the problem of how to produce a unitthat is of approximately the same size as a conventional ceiling rose.The articles that have been provided previously are still far largerthan the standard type of ceiling rose that is installed in the majorityof domestic housing causing the modified ceiling roses to be detrimentalto the decor of the house. Hence, such articles have not been widelyused domestically.

Thus, to date, an acceptable ceiling rose combined with a smoke detectorhas not been available. It would be desirable to provide a satisfactoryarticle to assist in persuading a person to install such a device ordevices in their home thereby improving the safety of the home for theoccupants thereof.

Furthermore, standard domestic smoke detectors require smoke toaccumulate to a significant level before the smoke detector present inthe housing is activated, thereby raising the alarm. It would bebeneficial if a unit could be produced that raises the alarm at a lowerlevel of smoke accumulation.

It is an object of the present invention to provide an improved smokedetector unit that aims to overcome, or at least alleviate, theabovementioned drawbacks.

It is a further object of the present invention to provide an improvedcombined ceiling rose and smoke detector that aims to overcome, or atleast alleviate, the abovementioned drawbacks.

Accordingly, a first aspect of the present invention provides a smokedetector unit, the unit comprising a housing containing a smoke detectorand at least two component mounting boards in stacked arrangement, thehousing having at least one air gap, wherein one of the boards isinverted with respect to the other and the detector is positioned on thelower board whereby, in use, the detector extends upwardly between saidboards.

The inverted stacked arrangement of the component mounting boardsprovides a reduction in the size of unit. The smoke detector ispreferably in the form of a smoke chamber having tapered sides. Furtherfunctional accessories would be included within the housing, asrequired, such as a sounder, control circuit and power supply (such as abattery).

The components mounted on the mounting boards are preferably arranged toachieve maximum utilization of the space provided on and between thecomponent mounting boards, thereby enabling further miniaturization ofthe unit. It is to be appreciated that the components should be arrangedin such a manner as to allow air to flow through the unit.

The component mounting boards preferably comprise printed circuit boards(PCBs). More preferably, the smoke detector and sounder are provided onopposing PCBs.

Preferably, the housing is attachable to a surface, such as a ceiling,via a base plate that may be fastened to the ceiling. Preferably, thehousing is in the form of a truncated cylinder closed by a circularbridging member. The base plate is preferably a circular plate of asimilar diameter to the housing.

Preferably, one of the printed circuit boards (PCBs) is attached to thebase plate and the other PCB is attached to the bridging member of thehousing whereby, when the housing and base plate are fastened together,the PCBs are in a parallel, stacked arrangement with the smoke detectorlocated on the PCB attached to the bridging member.

The housing and baseplate may be connected by any suitable means butpreferably screw together. More preferably, the housing and baseplateare attached by means of a bayonet fixing. More preferably still, one ofthe parts is provided with a retaining barb that fits into acomplimentary slot or recess provided in the other part, therebyenabling the two parts to be locked together.

Preferably, an air gap is provided between the upper edges of thehousing and the base plate to allow air to enter the interior of thehousing.

In an alternative embodiment of the present invention, the housing maycomprise a cover and a mounting plate, the mounting plate beingattachable to the base plate. Preferably, the mounting plate supportsthe component mounting boards in a stacked arrangement, the boardshaving the required functional accessories thereon. More preferably, themounting plate has legs extending therefrom which allow the PCBs to besupported in a stacked arrangement, the smoke detector being located onthe PCB furthest from the plate. Preferably, the mounting plate may beencased by the cover to protect the contents thereof. Preferably, themounting plate is a circular plate and the cover is in the form of acup-shaped unit that fits over the plate. The mounting plate and coverare preferably sealed together to prevent access being gained to thecomponents of the housing. Preferably, the air gap is provided betweenthe sides of the plate and the upper edges of the cover.

In a preferred embodiment of the present invention, the housing or coveris also provided with a transparent region whereby an emergency lightmay be contained within the unit and may shine through the transparentregion upon activation thereof. Preferably, the transparent region is inthe form of a transparent ring that extends around the periphery of thecover. Further components may be included within the unit to provide amulti-functional device, such as a carbon monoxide detector, heatdetector and/or intruder detector.

The housing may be in the form a ceiling rose. Preferably, a centralhollow shaft is provided through the housing for passage of the cablefor the mains light that depends from a ceiling rose.

Accordingly, a second aspect of the present invention provides acombined ceiling rose and smoke detector unit, the unit comprising ahousing in the form of a ceiling rose, the housing containing a smokedetector and at least two component mounting boards in stackedarrangement, the housing having at least one air gap, wherein one of theboards is inverted with respect to the other and the detector ispositioned on the lower board whereby, in use, the detector extendsupwardly between said boards.

The appropriate electrical wiring for the functional accessories and/orthe mains light may be provided on or within the base plate forconnection to conventional mains wiring that extends from the ceiling.Alternatively, the appropriate wiring may be contained within thehousing. More preferably, the outer side of the mounting plate isprovided with wiring connections and the base plate is preferablyprovided with an aperture for passage of these wires but is free fromany wiring connections.

To this end, a third aspect of the present invention provides anelectrical accessory comprising a housing with a mounting plate, theplate being connectable to a baseplate for mounting to a surface whereinelectrical connections are provided in the housing and the baseplate isprovided with an aperture therethrough for passage of wiring to saidelectrical connections.

The housing preferably comprises a mounting plate and cover. Preferably,the electrical connections are provided on the mounting plate andelectrical wiring therefrom extends from the mounting plate into thecover and is retained therein. Preferably, electrical pins or terminalsextend from the mounting plate for connection to a complimentary socketprovided at the ends of the wiring.

A fourth aspect of the present invention provides an electricalaccessory comprising at least one detector for detecting a potentialhazard, the detector being in communication with a mains light fittingwhereby detection of a hazard switches on the mains light.

The detector may detect any type of potential hazard by means of anappropriate sensor. For example, the detector may be a smoke, gas and/orheat detector. Alternatively or additionally, the detector may be in theform of an intruder detector, e.g. in the form of infra-red sensorsand/or video-surveillance cameras.

Alternatively or additionally, the detector may be one that detects amalfunction in one or more of the other potential hazard detectors. Itis to be appreciated that more than one detector would need to beincluded in this type of accessory. For example, a smoke detector may beprovided in an accessory with additional means for detecting if thesmoke detector is no longer working e.g. due to battery failure, whichactivates the mains light to alert the occupants that the batteryrequires replacement.

Preferably, the mains light remains on for as long as the hazard isdetected, for example, for as long as smoke is detected or until amalfunctioning detector is repaired. The mains light may flash for apredetermined number of seconds prior to being switched on continuously.

It is preferable to provide an emergency light that is activated uponfailure of the mains light. For example, if there is a power failure orfire in the building burns out the mains light power supply, anemergency light is automatically activated instead of the mains light.Preferably, the emergency light also forms part of a ceiling rose fromwhich the mains light depends. It is preferable for the accessory toalso include a detector for activating the mains light at any timeshould the emergency light be inoperable.

The detectors may communicate with the mains light and/or emergencylight through any appropriate means, such as hard-wiring, a centralisedcomputer system and/or radio waves, such as FM-technology

A system of such electrical safety accessories may be providedthroughout a building whereby detection of a hazard by at least one ofthe detectors switches on a mains light.

Yet a further aspect of the present invention provides an electricalaccessory comprising at least one detector for detecting a potentialhazard, the detector being in communication with an intruder alarm panelwhereby detection of a hazard by the electrical accessory activates theintruder alarm and/or detection of an intruder by the intruder alarmactivates an alarm provided in the electrical accessory. Preferably,activation of the alarm in the electrical accessory also results in themains light being switched on.

The electrical accessory may also be linked to a telephone line whereby,upon detection of a hazard, such as fire, a preselected telephone numberis dialed, such as that of the appropriate emergency service.

For a better understanding of the present invention and to show moreclearly how it may be carried into effect, reference will now be made byway of example only to the accompanying drawings in which:

FIG. 1 is a cross sectional view through a conventional smoke detectorunit;

FIG. 2 is a side view of the smoke chamber included in the smokedetector unit of FIG. 1;

FIG. 3 is a side view of a smoke chamber for including in a smokedetector unit according to the present invention;

FIG. 4 is a cross sectional view of a smoke detector unit according toone embodiment of the present invention that includes the smoke chambershown in FIG. 3;

FIG. 5 is a cross sectional view of a smoke detector unit according toanother embodiment of the present invention that includes the smokechamber shown in FIG. 3;

FIG. 6 is a perspective view of a smoke detector unit according to athird embodiment of the present invention;

FIG. 7 is an exploded view from above of the smoke detector unit shownin FIG. 6;

FIG. 8 is an exploded view from below of the smoke detector unit shownin FIG. 6;

FIG. 9 is a perspective view from above of one of the component parts ofthe smoke detector unit shown in FIG. 6;

FIGS. 10 and 11 are respectively a top and bottom perspective view of afurther component part of the smoke detector unit shown in FIG. 6;

FIGS. 12 and 13 are respectively a top and bottom perspective view ofthe baseplate component of the smoke detector unit shown in FIG. 6;

FIGS. 14 and 15 are respectively a top and bottom perspective views ofyet a further component part of the smoke detector unit shown in FIG. 6;

FIG. 16 is a perspective view of a smoke detector unit according to afourth embodiment of the present invention;

FIG. 17 is an exploded view of the smoke detector unit shown in FIG. 16;

FIG. 18 is a perspective view from below of two of the components of thesmoke detector unit shown in FIGS. 16 and 17, when assembled; and

FIG. 19 is an exploded side view of the smoke detector unit of FIGS. 16to 18, having the functional components included therein.

Referring to FIGS. 1 and 2 of the accompanying drawings, a conventionalsmoke detector unit 2 with a smoke chamber 4 is illustrated. The smokechamber 4, sounder 6, control circuit and power supply are mounted on asingle printed circuit board 8 that is secured to a base component 10. Acover 12 is connectable to the base component having air gaps 14provided in the base of the cover to allow air to flow through the unitfor detection of smoke. However, these types of unit are unsightly dueto their large size being dictated by the dimensions and layout of thecomponents within the unit.

FIGS. 3 and 4 of the accompanying drawings illustrate one embodiment ofa smoke detector unit according to the present invention. The unit 20again has a base plate 30 having a printed circuit board 28 mountedthereon and a cover 32 comprising an open-ended cylinder closed by abridging member. An air gap 34 is provided between the upper edges ofthe cover and the base plate to allow air to flow into the unit (asillustrated by the arrows in FIG. 2). Additionally, a second printedcircuit board (PCB) 36 is provided mounted internally on the bridgingmember of the cover whereby the smoke chamber 24 is mounted on thisboard and the alarm sounder 26 is mounted on the opposing PCB 28. Thefirst PCB 28 is inverted with respect to the second PCB 36 such that thecomponents provided on the first PCB extend downwardly and thecomponents provided on the second PCB extend upwardly. Such anarrangement is important in providing a unit of smaller dimensions thanhas been provided prior hereto. Such an arrangement has not beenenvisaged previously because the large number of components that have tobe placed on the boards would suggest that such an arrangement would notbe feasible. Whilst simple stacking of the boards on top of each othermay be considered a viable option, this type of stacking would lack theimportant advantage provided by the arrangement of the presentinvention, being the substantial reduction in size of the final article,both in width and in depth.

The provision of the components on each board facing inwardly towardseach other may be expected to create difficulties with the flow of airthrough the unit which is required for the smoke detector housed thereinto operate efficiently. However, by the provision of the stackedarrangement having the smoke detector on the lower PCB extendingupwardly, the remaining components can be arranged such that an adequateair flow to the smoke detector is achieved.

Additionally, the smoke chamber 24 is provided with tapered sideswhereby the chamber has the same height and is of the same diameter asthe smoke chamber shown in FIGS. 1 and 2 but has a reduced diameter atthe top of the chamber. In this respect, the dimensions “D” and “H” ofthe smoke chambers (see FIGS. 2 and 3) are critical to achieve therequired performance of the smoke detector. The larger the smokechamber, the better the performance. However, by tapering the walls ofthe chamber, as shown in FIG. 3, the total volume occupied by thechamber is reduced compared to that shown in FIG. 2 whilst theperformance achieved is substantially the same. I.e. the taperedconfiguration provides an air space around the smoke detector within theunit which allows any smoke in the air to circulate and enter the smokedetector. This assists in ensuring that adequate air circulates throughthe inverted, stacked arrangement of the components in the unitaccording to the present invention. The provision of an air space in theprior art, where the smoke detector is mounted on the base, alsodictated that the cover had to be larger than the base to allow air tocirculate within the unit, again leading to an increase in the size ofthe unit.

In this manner, the design and layout of the components in the smokedetector unit shown in FIG. 4 is such that an overall reduction of atleast 10% in the size of the smoke detector unit can be achieved with nodeterioration in detection and airflow performance.

Furthermore, the smoke chamber now extends upwardly in a unit that isprovided with an air space near to the extreme upper limits of thedevice. Hence, when the device is attached to a ceiling, the unit ismore susceptible to smoke detection since the entry points for air toflow into the unit are higher and thus, smoke does not have to build upto such a significant level before entering the unit. Previously, theentry points have been along the sides of the housing or in the bridgingmember which, in use, is situated further from the ceiling.

Utilization of interconnected PCB design areas enables the unit to beminiaturized even further since the sounder, control and power supplycircuits can be designed to fit on both PCBs. This enables the diameterA to be reduced by at least 16% of the diameter of a conventional smokedetector unit (see FIG. 5) when space is not required in the centre ofthe unit for placing additional components or for the passage of, forexample, wiring for a light depending from the unit. The base can besmaller in diameter because the smoke detector is mounted at a positionspaced from the base.

The arrangement of the component mounting boards and the location of thesmoke detector has further implications in addition to improving theperformance of the smoke detector and providing a smaller, aestheticallypleasing device for mounting on a ceiling. The stacking of the boardsalso enables further safety features to be included within the unitand/or allows for smoke detectors to be combined with other appliances,such as a domestic ceiling rose, in a product that is of an acceptablesize to the domestic marketplace.

Referring to FIG. 6 of the accompanying drawings, a smoke detector unit40 according to another embodiment of the present invention isillustrated. FIG. 6 shows the assembled unit 40 that contains theprinted circuit boards, smoke chamber, sounder, control circuit andpower supply. The unit comprises three main parts, a base plate 42, amounting plate 44 and a cover 46. The base plate 42 is the part that maybe attached to a surface, such as a ceiling. The mounting plate 44supports the printed circuit boards (PCBs) carrying the functionalcomponents, such as the smoke chamber, sounder and control circuit, thePCBs being provided in a stacked arrangement on the plate. The cover 46is then placed over and fixed to the mounting plate to encase thecomponents. The cover and plate are then attached to the ceiling byconnecting the mounting plate to the base plate.

FIGS. 7 to 15 show the various components in further detail andillustrate their interconnection. For the sake of simplicity, theinternal functional components, such as the printed circuit boards,smoke chamber and sounder are omitted from these Figures to illustratethe construction of the unit. The base plate 42 (see in particular FIGS.7, 8, 12 and 13) is flat and generally circular and has a central region52 in the shape of a sector circle that is relieved of material. Spacedinwardly from the perimeter of the plate is an annular flange 54 thathas a ridge or thread 56 extending outwardly therefrom around tworegions of the flange, one of the threads terminating in a flexible maleportion or retaining barb 55. A section 57 of the rim is solid. The baseplate is also provided with a number of holes 58 for insertion of fixingmeans to enable the device to be attached to a surface, such as aceiling.

The mounting plate 44 is a circular plate of similar dimensions to thebase plate and has arcuate side walls. Three parallel locating legs 60extend substantially perpendicularly from the plate 44 (see, inparticular FIGS. 7, 8, 10 and 11). Each of the legs is provided with asmall foot 62 extending inwardly. The printed circuit boards (not shown)are stacked within the boundary of the legs, a first board being locatedon the plate of the component and a second board being held in a spacedorientation relative to the plate near to the end of the locating legs.The smoke detector (not shown) is located on the board furthest from theplate near to the ends of the legs, extending inwardly towards theplate. The opposing side of the plate is provided with an annular flange64 extending around two-thirds of the plate. Two opposing sections ofthe flange have a projecting rim 66 and a hole 68 is provided in theregion of the plate that is flangeless. Additionally, the plate hasholes 67 that are surrounded on one side by an open-sided box 69.

The cover part 46 of unit is generally in the form of a truncatedcylinder, having slightly tapered sides 70 and a circular bridgingmember 72. The mouth of the cover is substantially the same diameter asthe mounting plate 44. An annular recess 76 extends around the perimeterof the bridging member and has three slots 78 of a similar width to thelegs of the mounting plate. Larger slots 80 are also provided at spacedapart intervals in the recess. Additionally, an aperture 82 is providedthrough the non-recessed part of the bridging member through which alight may shine to demonstrate that the components contained within theunit are charged and a series of slots 84 are provided that correspondto the positioning of a speaker provided within the housing.

The mounting plate and cover are fixed together by placing the ends ofthe legs 60 through the complimentary slots 78 provided in the annularrecess 76 of the cover. The feet retain the mounting plate within thecover. A transparent ring 90 (see FIGS. 14 and 15) is placed over therecess and secured thereto by means of projections 92 having feet 94that also pass through the slots 78. The mounting plate is then securedto the base plate by a bayonet type fixing wherein the mounting plate ispushed onto the baseplate and twisted such that the flexible maleportion or retaining barb 55 of the baseplate slots into the hole 68 ofthe mounting plate to lock the two together. The arcuate side walls ofthe mounting plate provide an air gap between the plate and the topedges of the cover to allow air to flow into the unit.

As mentioned, all the components for operation of the smoke detector andany other functions the unit may perform are contained within thehousing formed by the mounting plate and cover. The mounting plate isprovided with holes 67 for the passage of any wiring and power may besupplied to the unit through wires that pass from the ceiling, throughthe central region of the baseplate into the mounting plate. A wiringconnection may be provided on the outer side of the mounting plate forconnection to the mains wiring. An emergency light may be containedwithin the unit, with the transparent ring allowing light to radiatefrom the interior of the unit via holes 80 in the bridging member of thecover.

The unit may also be provided as part of a ceiling rose, as illustratedin FIGS. 16 to 18 of the accompanying drawings. Features that areidentical to those in FIGS. 6 to 15 are given the same referencenumerals and only the differences will be discussed in detail. Themounting plate 44 is provided with a hollow shaft 100 that extends fromthe centre thereof which is substantially parallel to the leg 60.Additionally, the bridging member of the cover has a circular hole 102through the centre thereof and a conical shaped hollow projection 104 isattached thereto. In this manner, the standard lighting cable can passthrough the centre of the device and extend through the hollowprojection for attachment of a pendant light. The device mimics theappearance of a conventional ceiling rose for a pendant type lightfitting.

With a conventional ceiling rose, it is common to provide the base withloop-in wiring connections and to have the cover enclose these and beprovided with an aperture to accommodate the wire for the pendant dropand indeed such an arrangement may be utilized in a unit according tothe present invention. However, it is to be noted that in the third andfourth embodiments of the present invention, the base 42 has no wiringconnections. Instead, these are provided in the assembly comprising themounting plate and cover, more particularly a special wiring connectionis provided at the end of the mains wiring extending from the ceilingthat plugs into connections projecting from the mounting plate. Hence,the provision of the cut out sector in the base plate allows mainswiring extending from the ceiling to pass therethrough to be connectedto the wiring contained within the cover and mounting plate assembly.

FIG. 19 of the accompanying drawings demonstrates how the functionalcomponents for a combined ceiling rose and smoke detector may beincorporated into the unit shown in FIGS. 16 to 18. Again, identicalfeatures to those already described in relation to FIGS. 16 to 18 havebeen given the same reference numerals and only the additional featureswill be discussed in detail. The stacked printed circuit boards (PCBs)300, 400 are provided with the necessary functional components, such asa battery 206, smoke chamber 208 and sounder 212. The smoke chamber hastapered sides and is positioned on the lower board 400 extendingupwardly towards the top circuit board. A circular central region (notvisible) of both PCBs is relieved of material and the space betweenthese regions is free of components to enable the passage of the hollowshaft 100 of the mounting plate 44 through which wires may be passed.The upper PCB 300 is also provided with electrical connections in theform of pins 204.

The stacked PCBs having the appropriate components secured thereto arethen fixed to the mounting plate 44 and housed within the cover 46. Thecover and mounting plate may then be attached to a baseplate 42 that isfastened to the ceiling. Mains wiring from the ceiling passes throughthe gap 52 in the baseplate and terminates in an input socket connector200 that may be connected to the pins 204 extending from the upper boardthrough the mounting plate.

It is clear that the large number of components contained between themounting plates 300, 400 would suggest that this stacked arrangementwould not be possible. However, with careful orientation of thecomponents, a fully assembled unit may be provided that is substantiallythe same diameter as a standard ceiling rose and has sufficient air flowthrough the unit.

It is to be appreciated that the ability to provide a smoke detectortogether with one or more other functional accessories that issubstantially the same diameter as a conventional ceiling rose willenable such devices to installed in domestic housing with minimal effecton the decor of the house. It is envisaged that all rooms of the housewill be provided with such units which may intercommunicate to enable analarm to be activated in the event that a hazard, such as smoke or gasis detected in any one of the rooms. The sounder in each unit may beactivated upon detection of a hazard by a unit in another room.

Units containing different types of hazard detector may be provided indifferent rooms. For example, a kitchen unit should contain a gasdetector (such as a carbon monoxide detector) rather than a smokedetector. Additionally, it is preferable for units that are placed inchildrens' rooms to be provided without a sounder such that only theemergency light is activated or, if the mains power is stilloperational, the mains light is switched on, rather than an audiblealarm that would scare a child and lead to panic. A further feature ofthe unit may be to include means whereby if one of the hazard detectorscontained within the housing fails, or the battery becomes flat, themains light depending from the rose is switched on to alert occupants ofthe house to the fault.

Each of the units throughout a building may also be connected via thehouse wiring to a control box that is linked to a telephone linewhereby, if one or other of the detectors in one or more of the units isactivated, a preselected telephone number, such as that of the localfire authority, is dialed thus enabling the appropriate emergencyservice, such as the fire brigade, to be alerted to the situation andpromptly arrive at the premises. The control box may enable more thanone telephone number to be rung. For example, one number could be to thehouse owner's telephone that provides a pre-recorded message over thephone warning the owner of the activation of the alarm. The owner thenhas the option to prevent a signal being sent to a local emergencyservice by pressing a pre-selected number of the phone. If this numberis not selected, the control box automatically dials the second numberof the emergency service.

Furthermore, the smoke detector unit may be linked, by means of anadditional wire or radio technology, to a burgler alarm panel containedwithin the building whereby, detection of smoke by the unit activatesnot only the alarm in the unit itself but also the burgler alarm. Thiswill result in the occupants of the house being alerted to the fire bytwo separate alarms. Similarly, detection of an intruder by the sensorsof the burgler alarm would activate both the burgler alarm and the alarmcontained in the smoke detector units. The smoke detector unit may thenswitch on the main light in the room. This would have the effect that ifa thief entered a property and activated the burgler alarm, all thelights in the property would also be switched on causing the intruder toflee.

1. A smoke detector unit comprising a housing containing a smokedetector and at least two component mounting boards in stackedarrangement, the housing having at least one air gap, wherein one of thecomponent mounting boards is inverted with respect to the othercomponent mounting board with the components mutually opposing, and thedetector is positioned on the lower component mounting board whereby, inuse, the detector extends upwardly between the opposing componentmounting boards.
 2. A smoke detector unit as claimed in claim 1 whereinfurther functional accessories are included within the housing.
 3. Asmoke detector unit as claimed in claim 2 wherein the functionalaccessories include a sounder, control circuit and power supply.
 4. Asmoke detector unit as claimed in claim 3 wherein the smoke detector andsounder are provided on the opposing component mounting boards.
 5. Asmoke detector unit as claimed in claim 1 wherein the smoke detector isin the form of a smoke chamber having tapered sides.
 6. A smoke detectorunit as claimed in claim 1 wherein the components are mounted on thecomponent mounting boards in such a manner as to allow air flow throughthe unit.
 7. A smoke detector unit as claimed in claim 1 wherein thecomponent mounting boards are printed circuit boards.
 8. A smokedetector unit as claimed in claim 1 wherein the housing is attachable toa surface via a base plate.
 9. A smoke detector unit as claimed in claim8 wherein the housing is a truncated cylinder closed by a bridgingmember.
 10. A smoke detector unit as claimed in claim 9 wherein one ofthe component mounting boards is attached to the base plate and theother component mounting board is attached to the bridging member of thehousing whereby, upon fastening of the housing and base plate together,the component mounting boards are in parallel, stacked arrangement withthe smoke detector located on the component mounting board attached tothe bridging member.
 11. A smoke detector unit as claimed in claim 8wherein the base plate is a circular plate of similar diameter to thehousing.
 12. A smoke detector unit as claimed in claim 8 wherein thehousing and base plate are attached to each other by means of a bayonetfixing.
 13. A smoke detector unit as claimed in claim 12 wherein one ofthe parts is provided with a retaining barb that fits into acomplimentary slot or recess provided in the other part, therebyenabling the two parts to be locked together.
 14. A smoke detector unitas claimed in claim 8 wherein the air gap is provided between upperedges of the housing and the base plate to allow air to enter theinterior of the housing.
 15. A smoke detector unit as claimed in claim 8wherein the housing comprises a cover and a mounting plate, the mountingplate being attachable to the base plate.
 16. A smoke detector unit asclaimed in claim 15 wherein the mounting plate supports the componentmounting boards in a stacked arrangement, the component mounting boardshaving the required functional accessories thereon.
 17. A smoke detectorunit as claimed in claim 16 wherein the mounting plate has legsextending therefrom which allow the component mounting boards to besupported in a stacked arrangement, the smoke detector being located onthe component mounting board furthest from the plate.
 18. A smokedetector unit as claimed in claim 15 wherein the mounting plate isencased by the cover.
 19. A smoke detector unit as claimed in claim 18wherein an air gap is provided between the sides of the mounting plateand the upper edges of the cover.
 20. A smoke detector unit as claimedin any one of the preceding claims wherein the housing is provided witha transparent region hereby an emergency light is contained within theunit.
 21. A smoke detector unit as claimed in any one of the precedingclaims wherein the housing includes one or more accessories selectedfrom the group consisting of a carbon monoxide detector, a heat detectorand an intruder alarm.
 22. A smoke detector unit as claimed in any oneof the preceding claims wherein the housing is in the form of a ceilingrose.
 23. A smoke detector unit as claimed in claim 22 wherein a centralhollow shaft is provided through the housing for passage of cable for amains light that depends from the ceiling rose.
 24. A smoke detectorunit as claimed in claim 1, wherein the housing comprises a mountingplate, the plate being connectable to a base plate for mounting to asurface wherein electrical connections are provided in the housing andthe base plate is provided with an aperture therethrough for passage ofwiring to said electrical connections.
 25. A smoke detector unit asclaimed in claim 24 wherein the housing comprises a mounting plate andcover, the electrical connections being provided on the mounting plateand electrical wiring therefrom extends from the mounting plate into thecover and is retained therein.
 26. A smoke detector unit as claimed inclaim 25 wherein electrical pins or terminals extend from the mountingplate for connection to a complimentary socket provided at the ends ofthe wiring.
 27. A combined ceiling rose and smoke detector unitcomprising a housing in the form of a ceiling rose, the housingcontaining a smoke detector and at least two component mounting boardsin stacked arrangement, the housing having at least one air gap, whereinone of the component mounting boards is inverted with respect to theother component mounting board with the components mutually opposing,and the detector is positioned on the lower component mounting boardwhereby, in use, the detector extends upwardly between the opposingcomponent mounting boards.
 28. A combined ceiling rose and smokedetector unit as claimed in claim 27 wherein appropriate electricalwiring for any functional accessories contained in the housing and/orfor a mains light that depends from the housing is provided on or withina base plate that is attachable to the housing for connection toconventional mains wiring extending from a ceiling.
 29. A combinedceiling rose and smoke detector unit as claimed in claim 27 whereinappropriate electrical wiring for any functional accessories containedin the housing and/or for a main light that depends from the housing isprovided on or within the housing and the housing is attachable to theceiling by a base plate.
 30. A combined ceiling rose and smoke detectorunit as claimed in claim 29 wherein a mounting plate is provided forconnection to the base plate, the mounting plate supporting thecomponent mounting boards and being encased in the housing, an intendedexterior side of the mounting plate being provided with wiringconnections.
 31. A combined ceiling rose and smoke detector as claimedin claim 30 wherein the base plate is provided with apertures forpassage of the wiring but is free from any wiring connections.